Professional treasure-hunting divers have found $4.5m worth of Spanish gold coins in shallow waters off Florida's Atlantic coast.

This has been a stunning discovery with photographs and videos of the 300-year-old cache showing the sparkling hoard as if the coins were newly minted.

A young Irishman dives at small islands in the Caribbean to photograph marine life off golden sands bereft of tourists. He may dream of finding his own gold fortune.

I am watching a leather-backed turtle casually making a turn towards the surface in crystal water, courtesy a smart-phone image sent by the diver. The colours of seabed plants, fish and rocks are amazing. Ominous, though, was a dark image of a shark where a lagoon met the tide.

This man dives and takes pictures unaccompanied. It seems risky. The images he collects may end as picture postcards. For now, however, it is a hobby.

Diving to observe marine life is a more chilly and cumbersome business around the island of Ireland. It is as serious an undertaking by the wet-suited participants as it is by those lucky ones in the balmy waters of the West Indies.

I have never dived though I have met many who have. There are risks. One man I knew was shot at by a fisherman from a pier who thought he was a seal. He missed.

Others I have seen returning to piers bearing spider crabs - not much to eat there, I thought - and the occasional sea urchin. This spiny shell looks attractive when dried and used to be common on the shelves of harbour bars.

The creature within was always something of a mystery until once, in an oyster-cleansing plant, I learned there was an export trade to Paris. Just what will the French not eat, I thought!

That was a long time ago when Charles Haughey, in a ministerial job, gave licences to urchin-gatherers as they could not be caught in pots. Such trade is now long gone.

One old salt remembered. He told me last week: "We used go out beyond (town named) when the boat was tied up. He (the collector) would get half-a-dozen lads together for a couple of days scouring rocky bays. In those days they (urchins) grew a decent size in the shallows and you could get to them by wading but areas got picked clean quickly and they never came back. We were ignorant in those days."

The urchins, filled with roe, were packed in polystyrene boxes, taken to Shannon to be flown to Paris. My man added, with the patient resignation of an old fisherman: "I don't know how much he made but all we got was beer money for the weekend."

In the 1980s, wild harvesting ended and an urchin aquaculture industry began, particularly on the south coast, and the lengthy, complex operation to produce juveniles began. This is still evolving.

According to Bord Iascaigh Mhara this is the only country to have commercial hatchery facilities - the tiny creatures go to other locations for on-growing. John Chamberlain, of Dunmanus Seafoods, Co Cork, has kindly invited me to take a look at the process sometime. Meanwhile, I read that in Galicia the creamy roe with scrambled egg is a treasured treat , while in Japan, 'uni-don', as it is called, with salmon eggs, is decadent perfection!